This disclosure generally relates to communication systems and methods, and particularly relates to leakage and side band signal suppression.
Most low cost two-way wireless communication systems generate baseband signals in a baseband frequency range. These signals are typically converted to an intermediate frequency or radio frequency (IF/RF) by a modulator device. An example modulator may be the AD8346 Quadrature Modulator from Analog Devices, Inc., which is a single-step analog up-converter that generates an L-Band (IF) signal from complex (in-phase and quadrature) baseband analog signals.
Such modulator devices are preferred due to their simplicity and low cost; however, these devices often have an L-band synthesizer (sine wave) signal and/or an opposite side band signal at the output, which can have deleterious effects on system performance. The L-band synthesizer signal is often referred to as “carrier bleed through” or “local oscillator (LO) leakage,” and the opposite side band signal is often referred to as the “negative image signal.” The LO leakage, although small compared to the desired output signal, can be a significant portion of the total output power. Additionally, the L-band synthesizer signal typically does not change in response to changes in the in-phase and quadrature baseband signal amplitude. The opposite side band signal is likewise small compared to the desired output signal, but may cause interference to a user operating in the frequency range of the opposite side band signal.
The LO leakage and opposite side band signals can be minimized by proper adjustment of the in-phase and quadrature input signals. Disclosed herein is an apparatus and method to measure the LO leakage and opposite side band signals. Also disclosed herein is an apparatus and method to adjust the input processing signals to a quadrature modulator to minimize the LO leakage and side band signals.